This study is a multicenter, randomized double-blinded clinical trial comparing zidovudine vs. ddI vs. a combination of zidovudine and ddI in symptomatic HIV-infected children ages 3 months to 18 years. The objectives are to compare the efficacy of therapy in the three arms of the study as determined by survival, disease progression, growth, neuropsychological development, development of opportunistic infections, etc., and to compare safety and tolerance of these agents in these children based on clinical and laboratory assessments.